1. Technical Field
The present invention relates to a labelled plastic vessel and a process for the preparation thereof. More particularly, the present invention relates to a labelled plastic vessel which has no bulge or wrinkle on the outer surface of an attached label and is excellent in the adhesion and peeling resistance of the label, and a process for preparing this labelled vessel by the in-mold labelling operation. Furthermore, the present invention relates to an adhesive label to be used for carrying out this process.
2. Description of the Prior Art
Attachment of a label indicating the content to a hollow-formed vessel is very important in the packaging technique because the attached label increases the commercial value of a packaged product and excites consumer's interest.
It has been known from old that a label is attached to a hollow-formed vessel by the in-mold labelling operation, and there is ordinarily adopted a method in which a label to be attached is held on the inner surface of a cavity of a forming mold by vacuum suction or the like and a plastic parison is subjected to hollow forming in this mold (see, for example, Japanese Patent Application Laid-Open Specification No. 202818/86).
A label composed mainly of a plastic film is preferable as the label to be attached by the in-mold labelling operation because the back surface can be printed and an image is sharp and excellent in the stain resistance. From the viewpoint of utilization of heat of the plastic vessel wall being formed, use of a heat-sensitive adhesive, especially a hot-melt adhesive, is advantageous.
However, in the case where a label composed of a plastic film is attached to a hollow-formed vessel by the in-mold labelling operation, wrinkling or bulging is caused in the label and the appearance characteristics of the label tend to degrade, and since the adhesion of the label to the outer surface of the vessel is insufficient, the label tends to peel or drop from the vessel during storage or transportation of the vessel. These tendencies are especially conspicuous in case of a composite label composed of a plastic film and a metal foil.
A heat-bondable film label of a plastic film comprising a hot-melt adhesive as the adhesive is disadvantageous in that in the in-mold labelling operation, it is often difficult to supply such labels precisely one by one and trouble with supplying a plurality of labels in the piled state to the side wall portion of a vessel is often caused. The reason is that since the smoothness of the film is high, adhesion is often caused between film labels and since the hot-melt adhesive is sensitive to heat, the stickiness is increased according to environmental conditions and the like.
An adhesive composed mainly of an ethylene/vinyl acetate copolymer, in which a tackifier is incorporated according to need, has been used as the hot-melt adhesive for labels. However, this known hot-melt adhesive is still insufficient in the heat resistance and chemical resistance. For example, in the case where hot filling is carried out for improving the preservability of the content (sterilization), deviation in a label or reduction of the bonding force tends to occur. Moreover, in case of vessels for cosmetics, toiletry goods, chemicals and the like, troubles such as peeling of labels and reduction of the bonding force are readily caused by the action of the content adhering to the outer surface of the vessel at the filling step. Gist of the Invention.
It is therefore a primary object of the present invention to prevent occurrence of wrinkling or bulging in a label in preparing a labelled plastic hollow-formed vessel by the in-mold labelling operation and improve the adhesion of the label to the outer surface of the vessel and the peeling resistance of the label.
Another object of the present invention is to provide a process in which the above-mentioned problems caused in preparing a labelled plastic vessel by the in-mold labelling operation are solved, it is possible to supply heat-bondable film labels separately one by one assuredly, and a strong bond can be formed between the label and the side wall of a plastic vessel being formed.
Still another object of the present invention is to provide a heat-bondable film label for the in-mold labelling operation, which has a capability of forming a beautiful and sharp printed image thereon, an excellent heat bondability and an excellent separate supplying property (anti-blocking property) in combination.
A further object of the present invention is to provide a label for the in-mold labelling operation, which can be attached to a polyolefin type plastic vessel with a high bonding strength by the in-mold labelling operation and can form a label-bonded portion having excellent heat resistance and chemical resistance.
In accordance with one fundamental aspect of the present invention, there is provided a process for the preparation of a labelled hollow vessel, which comprises blow-forming a single-layer or multiple-layer plastic parison or sheet in a blow mold having a label attached to the inner surface of a cavity thereof to bond the label to the surface of a side wall portion, wherein a label composed mainly of a drawn film of a plastic material having a heat shrinkage factor larger than the forming shrinkage factor of a plastic material constituting the outer surface of the vessel at a temperature (T.sub.1) lower by 40.degree. C. than the melting point or softening point of the plastic material constituting the outer surface of the vessel is used as the label.
In accordance with another aspect of the present invention, there is provided a labelled vessel comprising a plastic vessel formed by blow-forming and a label bonded to the surface of a side wall portion of the vessel by the in-mold labelling operation, wherein the label is a label comprising a drawn plastic film as the substrate and the label is bonded to the vessel so that the residual equilibrium shrinkage factor (Rs), defined by the following formula, of the drawn plastic film is in the range of from 0.5 to 100%: ##EQU1## wherein L.sub.1 stands for the length of the label film peeled from the vessel and L.sub.2 stands for the length of said peeled label film equilibriated at a temperature (T.sub.1) lower by 40.degree. C. than the melting point or softening point of the plastic material constituting the outer surface of the vessel.
The following labels are especially preferably used in the present invention.
(I) A heat-bondable film label comprising a plastic film layer, a print layer formed on the inner surface side of the plastic film layer, a hot-melt adhesive layer formed on the print layer and, if necessary, an overcoat layer formed on the outer surface side of the plastic film layer, wherein resin and/or inorganic beads having a particle size of 0.1 to 100 .mu.m are included in any of the print layer, the hot-melt adhesive layer and the overcoat layer, and in any of the surfaces, the center line average height (JIS B-0601) is in the range of from 0.2 to 50 .mu.m. Center line average height is calculated as center-line mean roughness.
Determination of Center-line Mean Roughness The center-line mean roughness, when the roughness curve has been expressed by y=f(x), shall be a value, being expressed in micrometers (.mu.m), that is obtained from the following formula, extracting a part of measuring length l in the direction of its center-line from the roughness curve, and taking the center-line of this extracted part as the X-axis and the direction of vertical magnification as the X-axis. ##EQU2##
Cut-off Value of Roughness Curve The cut-off value of the roughness curve, when a high-pass filter of -12 dB/oct in attenuation factor has been used in obtaining the roughness curve, shall be the wavelength corresponding to the frequency attaining a gain of 75%, hereinafter referred to as the "cut-off value."
Cut-off Values The cut-off values shall generally be the following six kinds: 0.08, 0.25, 0.8, 2.5, 8, 25 Unit: mm
Standard Values of Cut-off Values The standard values of the cut-off value, unless otherwise specified, shall be in accordance with the divisions in Table 1.
TABLE 1 ______________________________________ Standard Values of Cut-off Value in Determining Center-line Mean Roughness Range of center-line mean roughness Cut-off value Exceeding Max. mm ______________________________________ 12.5 .mu.m R.sub.a 0.8 12.5 .mu.m R.sub.a 100 .mu.m R.sub.a 2.5 ______________________________________
Remark: Center-line mean roughness shall be determined by firstly designating the cut-off values. In carrying out the designation or instruction of the surface roughness, as it is inconvenient to designate that on all such occasions, unless otherwise required to specify, values of this table shall be used. PA0 2. In the case where the measuring length is three times or more the cut-off value, the designation of the measuring length may be omitted. PA0 Remarks: PA0 1. The permissible maximum value mentioned here shall be an arithmetic mean value of R.sub.a on several points randomly extracted from the indicated surface, but shall not be the maximum value of individual R.sub.a value. PA0 2. The maximum value designation of the center-line mean roughness is 6.3 where "6.3 a" means 0 .mu.m R.sub.a .ltoreq.6.3 a.ltoreq.6.3 .mu.m R.sub.a. PA0 3. For the cut-off value in the case of the maximum value designation of the center-line mean roughness, a value corresponding to the maximum value in Table 1 shall generally be used. When any cut-off value other than this value is to be used, this value shall be appended. PA0 Example 1: In the Case where Standard Values of Cut-off Values for Upper Limit and Lower Limit (Table 1) Are Equal: A sectional designation when the upper limit of 6.3 .mu.m R.sub.a and the lower limit of 1.6 .mu.m R.sub.a shall be designated as (6.3 to 1.6) a. In this case, 0.8 mm shall be used for the cut-off value. PA0 Example 2: In the Case where Standard Values of Cut-off Values for Upper Limit and Lower Limit (Table 1) Are Different: A sectional designation when the upper limit of 25 .mu.m R.sub.a and the lower limit of 6.3 .mu.m R.sub.a shall be designated as (25 to 6.3) a. In this case, it means that a center-line mean roughness measured by a cut-off value of 2.5 mm is 25 .mu.m R.sub.a or under, and that a center-line mean roughness measured by a cut-off value of 0.8 mm is 6.3 .mu.m R.sub.a or over. PA0 Remarks: PA0 1. In the case where it is required to equalize the cut-off values corresponding to the upper and lower limits, or in the case where cut-off values other than standard values of Table 1 is to be used, the cut-off value shall be appended. In the case of Example 2, when the cut-off value corresponding to the upper and the lower limits is taken as 2.5 mm, it shall be designated as (25 to 6.3) a .lambda.c 2.5 mm. PA0 2. Center-line mean roughness of the upper and the lower limits mentioned here shall be the arithmetic mean values of R.sub.a at several points sampled randomly from the designated surface, but shall not be the maximum value of individual R.sub.a values.
Measuring Length The measuring length shall generally be a value of three times or more of the cut-off value.
Indication of Center-Line Mean Roughness (R.sub.a)
Designation of Center-Line Mean Roughness The designation of the center-line mean roughness shall be as follows: ##STR1## Remarks: 1. In the case where the value of the center-line mean roughness obtained by using the standard value of the cut-off value given in Table 1 is in the range shown in Table 1, the designation of the cut-off value may be omitted.
Preferred Number Series of Center-Line Mean Roughness When the surface roughness is designated by the center-line mean roughness, unless otherwise required, the preferred number series of Table 2 shall be used.
TABLE 2 ______________________________________ Preferred Number Series of Center-Line Mean Roughness ______________________________________ 0.013 0.4 12.5 0.025 0.8 25 0.05 1.6 50 0.1 3.2 100 0.2 6.3 -- ______________________________________
Maximum Value Designation for Center-Line Mean Roughness In the case where the surface roughness is designated by the permissible maximum value for the center-line mean roughness, it shall be represented by the numerical value selected from the preferred number series of Table 2, suffixing a.
Sectional Designation for Center-Line Mean Roughness If it is required to designate a center-line mean roughness in a certain section, numerical values corresponding to the upper limit (that of the larger designation value) and a lower limit (that of the smaller designation value) shall be stated additionally by selecting from Table 2.
(II) A heat-bondable film label comprising a plastic film layer, a print layer formed on the inner surface side of the plastic film layer, a hot-melt adhesive layer formed on the print layer and an overcoat layer of a release substance having a static friction coefficient smaller than 0.20, which is formed on the outer surface side of the plastic film layer.
(III) A label to be bonded to the outer surface of a polyolefin type plastic vessel by the in-mold labelling operation, which comprises a label substrate and an adhesive layer of chlorinated polypropylene formed on one surface of the substrate.
(IV) A label to be bonded to the outer surface of a polyolefin type plastic vessel by the in-molding labelling operation, which comprises a label substrate and an adhesive layer of a blend of chlorinated polypropylene and a copolymer of ethylene with a carbonyl group-containing ethylenic monomer, which is formed on the substrate on the surface to be bonded to the vessel.
(V) A label to be bonded to the outer surface of a polyolefin type plastic vessel by the in-mold labelling operation, which consists of a laminate comprising a transparent label substrate, a printing ink layer formed on the inner surface side of the label substrate and an adhesive layer of an ethylenic copolymer composed mainly of ethylene and containing an ethylenically unsaturated carboxylic acid or a derivative thereof as a comonomer, which is formed on the printing ink layer.
(VI) A label to be bonded to a polyolefin type plastic vessel by the in-mold labelling operation, which consists of a laminate comprising a transparent label substrate, a printing ink layer formed on the inner surface side of the label substrate, a primer layer composed of chlorinated polypropylene or a blend of chlorinated polypropylene and a copolymer of ethylene with a carbonyl group-containing ethylenic monomer, which is formed on the printing ink layer, and an adhesive layer of a copolymer composed mainly of ethylene and containing an ethylenically unsaturated carboxylic acid or a derivative thereof as a comonomer, which is formed on the primer layer.
The labels (I) and (II) are excellent in the heat bondability and separate supplying property, and the labels (III) through (VI) are excellent in the combination of the heat resistance and chemical resistance in the state bonded to a vessel.